Yes, I've bought several times from that website and they are reliable and if you pay for the express shipping, you'll have your order in 4 or 5 days. The lower cost shipping takes right at 2 weeks. I've used both.

Which lipos the 2S or the 3S ones?

Over on the TRX forums, they are asying the batt box dimensions are 101.9mm x 35mm x 20.3mm (length x width x tall). The hard dimension to fit is going to be the heigth.